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首页> 外文期刊>Computational Chemistry >On the Accuracy of the Complete Basis Set Extrapolation for Anionic Systems: A Case Study of the Electron Affinity of Methane
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On the Accuracy of the Complete Basis Set Extrapolation for Anionic Systems: A Case Study of the Electron Affinity of Methane

机译：阴离子系统完全基集外推的精度：以甲烷的电子亲和力为例

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Recent experimental evidence suggests again the existence of the metastable methane anion in plasma swarms. In order to test the reliability of the complete basis set (CBS) extrapolation scheme with augmented correlation-consistent basis sets for anionic molecules, we study the evolution of the electron affinity of methane with benchmark ab initio calculations with aug-cc basis sets up to aug-cc-pV6Z + diffuse. Geometry optimizations and vibrational analysis were done at the MP2 level. The electron affinity (EA) was calculated at the MP2 and CCSD(T) levels with and without frozen core and including the extrapolations to the CBS limit. Using the aug-cc-pVnZ basis sets it is found that two non-decreasing CCSD(T) CBS limits exist for the EA (0.29 and 0.53 eV) obtained with the n = 3, 4, 5 and n = 4, 5, 6 series, respectively. A new scheme is proposed which can be generalized for very accurate quantum chemical description of molecular anions: the standard aug-cc-pVnZ basis sets can be supplemented with extra-diffuse orbitals using a simple even-tempered scheme. This yields a reliable CBS extrapolation method to develop a (discrete approximation of a) continuum anionic state near ionization, viz., one that closely matches the energy of the corresponding neutral state. These results show that CH4 has no stable anions of 2A1 symmetry, implying that plasma swarms with anionic methane consist of metastable rather than stable methane anions.
机译：最近的实验证据再次表明，血浆群体中存在亚稳态甲烷阴离子。为了测试具有增强的相关性一致的阴离子分子的基础集的完整基础集（CBS）外推方案的可靠性，我们使用基准ab从头计算并使用aug-cc基础集来研究甲烷的电子亲和力演变aug-cc-pV6Z +扩散。在MP2级别上进行了几何优化和振动分析。电子亲和力（EA）是在MP2和CCSD（T）水平下计算的，有和没有冻结的核，并且包括对CBS极限的外推。使用aug-cc-pVnZ基集，发现在n = 3、4、5和n = 4、5、5时获得的EA（0.29和0.53 eV）存在两个不变的CCSD（T）CBS限制。 6个系列。提出了一种新的方案，该方案可以推广用于分子阴离子的非常精确的量子化学描述：可以使用简单的均匀退火方案，用超扩散轨道补充标准的aug-cc-pVnZ基集。这样就产生了一种可靠的CBS外推方法，可以在电离附近形成一种（离散近似的）连续阴离子状态，也就是与相应中性态能量非常匹配的阴离子状态。这些结果表明，CH4没有2A1对称性的稳定阴离子，这表明具有阴离子甲烷的等离子体群由亚稳态而不是稳定的甲烷阴离子组成。

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